Braking system



Aug. 25, 19257 1,551,401

B. w. JONES BRAKING SYSTEM Filed Feb. 14, 1925 Ihventor: BenjaminW.dones,

I His Attbr'n ey ing. It will be assumed that the motor is suitableconnected todrive an elevator, hoist, or the like, and that the motor isprovided with a suitable shunt field (not shown in the drawing). Thismotor is indicated as of the direct current type and it is arranged tobe connected to the source of supply 11 by means of the pairs ofreversing switches shown. The switches 12 and 13 are provided forconnecting the motor for the hoisting direction and the switches 14 and15 are provided for connecting the motor for the lowering direction.These switches serve to connect the motor to the source of supply forthe desired direction of motor operation, and while the switches areshown as of the manually operated type, it will be understood that Icontemplate that these switches may be operated in any suitable manneras, for instance, the switches may be of the elect-reins.gneticallyoperated or contactor type, and these switches may be operated under thecontrol of a suitable master switch.

The accelerating resistor 16 in the motor armature circuit is providedfor the usual purpote. The motor armature is arranged to be included ina dynamic brake circuit by means of the switch 17 and the variableresistor 18 is provided in the dynamic brake circuit for regulating thisbraking action. It will be understood that I contemplate that thevariation of the effective portions of the tors 16 and 18 and theoperation of the 17 may also be under the control of th. 2 mastercontroller (not shown). The motor control arrangement above described iswell known to those skilled in the art who supp y the desired mastercontroller 7 the various switches and for varying the above namedresistors in order to r"ect the desired control of the motor. I

' have not shown the details of such a remote control arrangement, forthe reason that it would ot help those skilled in the art to rerstanding of the invention since the on is directed primarily to theregui of the braking effect on the motor. The braking effect on themotor and the apparatus controlled thereby is supplied by the provisionof the dynamic braking circuit heretofore referred to and by means ofthe mechanical brake 19 which is of the type aris regulated byelectroresponsive means under the joint control of the generated voltageof the motor, the current in the brake winding and the current in themotordynamic brake circuit.

This electroresponsive means comprises the contactors 20 and 21 whichare provided for connecting the brake winding to the source of supply,the relays 22 and 23 which are provided with windings energized inaccordance with the generated voltage of the motor and the current inthe brake winding circuit so as to control the time at which thecontactors 20 and 21 open after the opening of the particular set ofdirectional switches so as to thereby maintain the brake windingconnected to the source of supply at a reduced value of energization andthus effect for a certain time interval a partial application of themechanical brake. The relays 22 and 23 are substantially identicaland-are each provided with two electromagnets and correspondingarmatures. The electromagnet 24 of the relay 22 is arranged to beconnected to the source of supply upon the closing of either of the lineswitches 12 or 14 so as to magnetically close the relay. Theelectromagnet 25 of this relay is provided with two coils, one coil 26being connected so as to respond to the potential applied to the motorwhen either line switch 12 or 14 is closed and to respond to thegenerated potential of the motor when the line switch which hadpreviously been closed is opened. The coil 27 of relay 22 is connectedin the circuit of the winding of the mechanical brake 19 under certainconditions, and these two windings 26 and 27 of the relay cooperate toeffect a joint control of the energization of the brake winding, as willbe hereinafter fully explained. V The two windings 26 and 27 arearranged to act cumulatively under certain conditions and to actdifferentially when this particular relay is governing the contactors 20and 21. The coils of relay 23 are connected in series with the similarcoils of relay 22 and these two relays are provided for accomplishingsimilar results at the time they are intended to function.

The relay 22 is arranged so as to function to effect a control of thebrake magnet winding when the directional switches 12 and 13 are closedand subsequently opened and the relay 28 is provided for effecting asimilar result when the directional switches 14 and 15 are closed andsubsequently opened.

The resistance, having the sections 28, 29, 30 and 31, is provided foreffecting a reduction of the energization of the brake magnet winding tolimit the heating of the winding and'to regulate the energizationthereof so as to effect a partial application of the brake. Thecontactor 32 is under the joint control of the directional switches 12and 14 so as to connect the brake winding directly to the source ofsupply. when the selected set in the drawing) for including the brakewinding in alocal circuitso as to regulate the application of the brake.

The contactor 35 is provided for controlling the local circuit in whichthe brake winding is included at a certain intervalin the application ofthe mechanicalbrake19, and this contactor is provided with a wind ing 36in the motor dynamic brake circuit and a winding 37 which 'is'connectedsimi:

'larly to the windings'26-of the relays 22 and 23. V I p i As thusconstructed and arranged and with the partsin their respective positionsshown in the drawing, the operationjot my invention is as follows:

Assume that it is desired motor in the hoisting direction. Thedirectional line switch es12 and-1'3 will be closed, thereby connectingthe motor armature to the source of supply- The contactors 20 and 21will be energized to close through the auxiliary switch 38 associatedwith the line switch 12, and the contactors 32 and 3twill be energizedthrough the auxiliary switch 39 associated with the line switch 12.; Thewinding of the electromagnet brake 19 will be energized and thebrake-will be fully released, the auxiliary switch 33 being there :uponopened so as to deenergize. the contactor 32 and connect the section 28of re sistance in series with the brake winding. When the directionalswitches 12'and 13 are closed the windings 24 of the relays 22 and 23and the windings 26 of these relays are energized from the source ofsupply so as to magnetically close the relay contacts. The closing ofthese relays at this time produces no eiiect on the energization of thebrake winding. It will be observed that upon the opening of thecontactors 32, the

winding 27 of the relays 22 and 2.3 will be included in the brakewinding circuit.

The winding 37 of the contactor' 35 is also energized across the supplycircuit by the closing of the directional switches 12 and '13 so thatthe contacts'of this contacton will automatically close upon the closingof the said line switches. Assume now that the motor has operated thedriven device to-the to operate the desired limit of operation, thedirectional switches 12 and 13 -w1ll be opened, thereby disconnectingthe motorfrom the source of supply and connecting the motor armature in,the dynamic brake circuit previously referred to.

Although the contactors 20'and 21 were previously closed in response-tothe closing I of the directional switch 12, these contactor's:

will not immediately open after the' op'enin'g of the co'ntactor 12,by'reason of the fact that the relays 22 and 23 are energized tomagnetically hold their respective contacts closed and thus establish amaintaining cire cuit' for these contactors 20 and 21.

The opening of thelineswitch 12 deenergizes theelectromagnets 2a of therelays 22 and 23 so that the-openingof these relays willbe under thecontrol of the r respective coils 26 and 27. 'For'this direction 01":motor operation the fluxes set upby the coils 26 and 27 01" relay 22will oppose each other,

'whereas the corresponding coils of relay'23' will set up fluxeswhichassist each other. The relay 23 will thus be maintained closed, but therelay 22 will automatically open when the diiierencebetween the flux setup 27 is less than apredeterminedvalue. It

will be observed that the deenergizatio'n of the co-ntactor 3t, due tothe opening of the directional switch 12, effects the inclusion of theresistor sectio'n'29 in series relation with the bralrewinding and theresistor sec tion 28 and simultaneously therewith the connection ofresistor sections 30 and 31 in multiple with the brake winding throughthe lower contact of the contactor 34C and the contacts of contactor-35. The contactor '35 will be maintained energized and closed y. reasonof the fact that the coil 36 of this contactor is energized by thecurrent in the motor dynamic bralre c rcuit and the coil 37 is energizedby the generated voltage of the H r The inclusion of the resistor 29 inseries motor.

with the'bralre winding and theresistor sections 30 andf31 in multiplewiththe brake winding effects a gradual reduction in the energization ofthe brake winding, thereby in turn effecting a partial application ofthe brake, v v I The generated voltage of the motor will graduallyreduce due to the lowering of the motor speed, and the current in thebrake winding also gradually decreases so that until the diflereneebetween the flux set up by the coil 26 and the'fiux set up by the coil27 of relay 22 has reduced to a predeter- .mined value, the relay 22will remain closed for an interval but will automatically open when thisdifference is the predetermined value, thereby deenergizing thecontacters 20'and 21 and effecting the disconnection of the'brakewinding from the source of supby the coil 26' and the fluXset up by'thecoil ply. The deenergization of the contactor 21 effects the closing ofa circuit through its lower contact 40, thereby shunting the resistorsection 31 and leaving the brake winding in a local circuit includingthe lower contact 11 of the contactor 3. the coils 27 of relays 22 and23, the brake winding, the lower contact 10 of contactor 21, resistorsection and the contacts of the contactor 35. A further gradualreduction of the current in the brake winding circuit is thus effectedby reason of the fact that the brake winding is disconnected from thesource of supply and included in a comparatively low resistance localdischarge circuit. By rea son of the inductive action of the brakemagnet, it will take an appreciable time interval for the brake to fullyapply, the local discharge circuit serving to provide a cushioningaction of the brake in setting.

WVhen the current in the dynamic brake circuit and the generated voltageof the motor have reduced to such a value that the coils 36 and 37 ofthe contactor will not maintain this contactor in its closed position,this contactor will open and thereby open the local discharge circuit toeffect a complete application of the brake.

The operation of the invention is the same when the set 01' directionalmotor switches 1 1 and 15 are closed for operation in the oppositedirection instead of the directional switches 12 and 18 as previouslydescribed for the hoisting direction. However, in this case the coils 26and 27 of the relay 22 will set up fluxes which are cumulative and thesimilar coils of relay 23 will set up fluxes which are differential withrespect to each other, so that the relay 23 will automatically open in amanner similar to the previously described operation of relay 22 todisconnect the brake winding from the source of supply and include thesame in the previously described local discharge circuit. This isbecause of the fact that the direction of the current through the brakewinding is the same as before but the generated )otential of the motorwill be in the opposite direction to that which was the case when themotor was operating in the hoisting direction.

It will thus be seen that the control of the application of themechanical brake is governed jointly by the opening of either thedirectional switches 12 and 1%, the generated voltage of the motor thecurrent in the brake winding circuit and the current in the motordynamic bralre circuit. The coils 27 of the relays 22 and 23 willfunction to give a time controlled regulation of the opera tion of theserelays, because of the fact that with the resistor sections 28 and 29 inseries relation with the brake winding and wit the resistor sections 30and 31 in shunt to the brake winding, the value of the current throughthe brake winding will gradually decrease to the value determined bythese resistances. The windings 27 of the relays are designed to set upfluxes which normally predominate over the fluxes set up by therespective coils 26. This will give a pure time function and the timefunction will be the predominating function. The energization of thecoils 26 of the relays 22 and 23 will be governed directly in accordancewith the generated voltage of the motor after the disconnection of themotor from the source of supply. This generated voltage will decrease asa neasure of the decrease of the motor speed. Thus, it the motor 10 isemployed for operating an elevator and if the elevator car is heavilyloaded and proceeding in the up direction, the overbalanced weight will.also be proceeding in the up direction. The action of gravity will beassisting the friction of the various parts to reduce the speed of theelevator car and this action of gravity will be cumulative with respectto the action of the mechanical brake 19 and the motor dynamic brakingeffect. Until the brake winding is disconnected by the source, the brakewill effect a partial braking torque. When the difference between thefluxes set up by the relay coils 26 and 27 of the particular relayintended to function "for this direction of operation (in the presentcase the relay 22) has decreased to the pr determ ned value, the relaywill automatically open its contacts, thereby disconnecting the brakewinding from the source of supply and including the same in a localdischarge circuit of relatively low resistance so as to effect a furtherapplication of the mechanical brake. By reason of the fact that the fluxof the coil 27 is the predominating flux of relay 22 and this fluxreduces at a definite rate, since the reduction of the generated voltageof the motor will decrease at a somewhat corresponding rate, thedifference between the fluxes will decrease a low rate and the operationof the relay will be relatively slow. This is desirable since the actionof gravity is assisting to bring the car to a stop and it is undesirableto apply too great a braking effect. The reduction of he currentin thebrake winding circuit when the brake winding is thus connected in thelocal disc large circuit, is again a true time function. The mechanicalbrake will be fully applied in all events after the expiration of thetime interval of the'reduction of the current in the brake windingdischarge circuit. However, this time interval may in certain cases betoo long and the motor may come to rest before this time interval haselapsed. It is desirable that the mechanical brake shall be fullyapplied when the motor and the elevator car have substantially stoppedso as to thereby avoid the well known settling action or dropping backof the elevator Joefore the brake is fully applied to hold the elevator.The contactor' prevents this settling action of the elevator because otthe fact that there will be an appreciable current in the motor dynamicbrake circuituntil the motor has practically stopped rotating and thecoil 36 of this con-tactor will be sufliciently energized to maintainthe contactor closed. However, when the motor has substantially stoppedrotating, the generated voltage of the motor will he very'small and thecoil .37 ofthe contactor'will he practically .deenergized and the coil36 of contactor will also be practically deenergized so thatthecontactor will automatically open its contacts, thereby opening thelocal discharge circuit in which thebrake winding is included and effectan immediate and full application ,of the brake.

In case the car wereproc eeding' in the up direction, lightly loaded, sothat the overba'lanced Weight was proceeding in the down direction, theaction of grayity on the counterweight will in this case attempt to keepthe car in motion. The coil 27 "of the relay 22 will again function-togive a time interval control of relay 22 the coil 26 will function asbefore to give a contake care of these conditions in the same .manner asthe relay 22 functioned ously to. take careofsimilar conditions-whentrol of the relay, dependent upon the speed I of the motor. 7 Since thegenerated vo'ltage of the motor will reduce at a relatively "low rate,the difference between the fluid-f coil 27' and coil 26 will reducecomparatively quickly so that the disconnection Off the brake windingfrom the source of supply will be effected in a shorter interval of timethan was the case when the overba lanced weight was proceeding in the updirec- .tion. This is desirable since theaction of gravityis in thiscase tending to keep the car .in motion and the braking effect -In-usthe comparatively great. will function as before to give a control of themechanical brake so that the brakewill be fully applied as soon as themotor has practically come to rest.

lVith the elevator car proceeding in the down direction, the relay 23willfu'nct ion instead of the relay 22 and the {functioning of thisrelay will produce similar results to those produced by the functioningof the relay 22 for the up direction. If the car is heavily loaded andproceedingi1i the down direction, the overha lanced weight will also be,mov'ing in the down direction and conditions will be present similar tothose encountered when the carwas proceed ing lightly loaded in the updirection. The relay 23 will function to automatically the car wasproceeding in the up directien I the e i s ine sn th wn The contactor35- previdirection lightly loaded, the overbalanced weight-will movingin the ffi iup ldirectiop and lconditions will'hefsimilar to theseencountered when the car was heavily loaded and prpceeding in the updirection. The relay will function to automatically-compen'sate ier thelvapiations in the laverbal- 'anced weight,-the speed .ofthe car and thedegree oflagppl-ica tion of the brake The contactor 35 also function :asbefore to effect. a iul l application of the mechanical :brake to holdthe elevator car .whenthe motor has practically come to rest. .7

It thusloe seen that the Ielays 2-2 and 23 effect an automaticregulation .of the apl of {the mechanical hnaike in accordance theconditions encountered at the t me the ginotor directional switches areopened tostop the page TFhe timing junction of these relays supplied zbythe relay coils 27 is the predominating iunction, {but the time intervalintroduced *in regulation of the brake windingais governed :by the rateat which the :gfillerateclvoltage of the motor decreases. The generatedvoltage-of the anotor will :decreaseias aifunction of the speed lof the.car' at the itime-thedi-rectiqi al switches are opened, the value ,oithe overbalanced weight and the direction in ,which this ioverbalancedweight is moving. Ittcau thus gbe seenithat these .relays automaticallyI take into account the ivariations in ethe onerbalanced weight.discriminate as between the overhalanced weight moving in the dow.ndirection .with the .car proceeding in the :up direction, the conditionin which the overbalanced weight xis' moving in the 11p direction with.the car proceeding in the up vdirection,the-condition in -\'vlllll theoverbalanced weight {is moving in the up direction with the carproceeding in t'he fdown direction, and the condition in which the.overbalanced weight is moving in the idown direction with the car pro-.ceedingin the same direction. The 91 erator'of the car need,therefolieilpay I10 tep-tlon to these various conditions encountered,since compensation ais :made therefor by the action of the relays.

' The contactor 35 is particularly usef during inching operations .ofthe eleyator. When the motor directional switch vnae-chan'ism isoperated so as to efiectaslight movement of the elevator car, thedynamic braking effect :of the motor will be comparatively small soathatthis vLcontactor will tunction to automatically every quickly open,-'the local discharge circuit for the zbrake minding so as to therebyeffect .acoIn-parat' cly quick application of the ":bllflikfifiltFY2151,- also: be understood :thatflunder theseiiccnditio s the ilelays22'Land s23 will fu nctiml t0 likewi eflect a comparatively .quickapplication of fthe'rbrakeaas isalesirabf, 7 7

patent statutes, I have described the principle of operation of myinvention, together with the apparatus which I now consider to representthe best embodiment thereof, but I desire to have it understood that theapparatus shown is only illustrative and that the invention can becarried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. In combination, a driving motor, means for applying a braking effectto the apparatus driven by the motor, electroresponsive switch mechanismfor controlling the value of the braking effect applied by said means, atiming device for controlling the said braking means, and means forregulating the time interval ofioperation of said device in accordancewith the speed of said motor.

2. In combination, a driving motor, a normally applied mechanical brakehavinga winding arranged to be connected to a source for releasing thebrake, means for controlling the energization of the driving motor tostart the motor and effect the connection of the brake winding to thesource, the said means being arranged to initiate a reduction of thecurrent taken by the brake winding from the source when the energizationof the motor is reduced to stop the motor, and means responsive to anoperating condition of said motor after the operation of said firstmentioned means to stop the motor for automatically disconnecting thesaid winding from the said source and connecting the same in a localcircuit to effect a greater degree of application of the brake.

3. In combination, a driving motor, a nor mally applied mechanical brakehaving a winding for releasing the brake, a resistance,electroresponsive switch mechanism for controlling the said resistanceand for controlling the connection of the said winding to a source ofsupply, and connections whereby the said resistance effects a reductionof the current taken by the said winding from the source to effect apartial application of the brake when the energization of said motor isreduced to stop the motor, and the brake winding is subsequentlydisconnected from the source of supply and included in a local circuitwith a portion of said resistance to increase the braking eflect.

4. In combination, a driving motor, a nor mally applied mechanical brakehaving a winding for releasing the brake, a resist- 'ance,electroresponsive switch mechanism for controlling the said resistanceand for controlling the connection of the said winding to a source ofsupply, and connections whereby the said switch mechanismis governed toinclude the said resistancein multiple with the saidwinding whilemaintaining the-connection of 'the'winding to thesource for an intervalafter the energization of said motor is reduced to stop the motor andthe said winding is subsequently disconnected from the source andincluded in a local circuit with a portion of said resistance.

5. In combination a driving motor, a nor mally applied mechanical brakehaving a winding for releasing the brake and for regulating theapplication thereof, switch mechanism for controlling the said winding,and means jointly controlled by the disconnection of the motor from thesource of supply, the generated voltage of the motor and the current inthesaid brake winding circuit for controlling the said switch mechanismto gradually reduce the energization of the said winding whilemaintaining the connection of the winding to the source for an intervalof time after the disconnection of the motor from the source and to thendisconnect the winding from the source to include the same in a localcircuit to further gradually reduce the energization thereof.

6. In combination, a driving motor arranged to be connected to asourceof supply,

a normally applied mechanical brake hav ing a winding arranged to beconnected to the source for releasing the brake, a resistance,electroresponsive switch mechanism for controlling the connection ofsaid winding to the source and for controlling the said resistance, andconnections whereby the said switch mechanism is governed to include aportion of said resistance in series with said winding and anotherportion thereof in multiple with the winding while maintaining theconnection of the winding to the source for an interval of time afterthe motor is disconnected from the source and to then disconnect thewinding from the source leaving the winding connected in a local circuitwith a portion of the resistance which was previously connected inmultiple with the winding.

7 In combination, a driving motor, a motor control switch forcontrolling the energization of the motor, a normally applied mechanicalbrake having a winding for releasing the brake, resistance forcontrolling the energization of the brake winding, electroresponsiveswitch mechanism for controlling the said resistance and the connectionof the said winding to a source of supply and connections whereby thesaid switch mechanism is governed to connect the said winding directlyto the source upon the closure of said motor control switch to start themotor and then include a portion of the said resistance in series withthe said winding when the brake is released, another portion of saidresistance is automatically connected in multiple circuit with the brakewinding with the multiple circuit in series with the remainder of theresistance upon the opening of said motor control switch to the source,leaving the winding included in a local circuit with asmall =portionofsaid resistance.

8. The combination in a system iorcontrolling an electric elevator,hoist, or the like, provided with a car and a counterweight therefor, ofa driving motor, directional switch mechanism for controllingtheenergizaticn of the motor to hoist or lower the car,- a normally appliedmechanical brake haying a winding for releasing the brake, andelectroresponsive switch mechanjism jointly controlled by saiddirectional switch mechanism, the generated voltageof the motor, and theValue of the current in the brake winding for regulating the energization of said brake winding in accordance with direction of movementof the said car and the direction of the movement of tile orerba'lancedweight of the ear and the counterweight. I

9. In combination, a driving motor, a mo- 7 tor control switch forcontrolling the energization off the motor from a source ofsupply,normallya'pp'lied mechanical brake having a winding for releasing thebrake, resistance for controlling the energization o -i' the brakewinding, electroresponsive switch mechanism controlled by the said motorswitch, the speed of the motor and the energization of the brake windingfor controlling the said resistance and .theconnection o'i'. saidwinding to a source of supply, and connections whereby the said switchmechanism is governed by the opening of said motor switch toautomatically conneetthe saiu resistance with said wind to reduce theenergization'oi the wind-' 'ii'l and after an interval. eflfect afurther ematic reduction of the energization of e brake winding. i

p 10,111 combination, a driving motor arranged to be connected to asource of sup- 41y, a line switch for connecting'the motor to thesource, a normally applied mechanical brake haying a winding arranged tobe connected to the source for releasing "the brake, a relay goyernedjointly bythe-generated oltage of the'motor and by the current in saidwinding for controlling the brake electrores 3-onsive switch mechanism 7v under the control of said line'switch and said relay, and connectionswhereby the opening of said line switch reflects a reduction of thecurrent in the brake winding and the said relay eii ects a furtherreduction of the current in the brake winding an interval after theopening ofsaid line switch.

1? In cqm iee ea s motor, a normally applied mechanical brake having awinding arranged to be connected to a source of supply to release thebrake upon the connection of :the motor. to the source, switch mechanlsm:for controlling the .con- .nectlon of said motor and said windmg to thesource, and means controlled by said motor for automatically reducingtheenerugization of the brake winding while mamtainingthecdnnectionthereof to the source .to effect a partial application ofthe brake for an ilfilZQlVill after the disconnect on of the motor fromthe source by the operation vof the brake by the operation, of anotherportion of said switch mechanism.

12. in combination, a dr ving motor, a motor control switch forcon-trolling the energization of the motor from a source of supply, anormally applied mechanical :brake having a winding arranged to ;beconnected to a source for releasingathe brake, means automaticallyconnected with the brake winding upon the opening of said motor switchfor reducing ;the energization of said winding to effect a partialapplication ofthe brake, and means automatically controlled in responseto the speed ,of ,the motor for completely deenengizing the said windingto reflect a full application of ,the brake when the motor haspractically stopped rotating; I

13. In combination, a driving motor ,ar-

ranged to be connected to a source of supply, a dynamic :braki-ngcircuit for the motor, a motor control switch for controlling theenergization of the motor from the said source, a normally appliedmechanical brake having a winding arranged to be connected .to a sourceof supply for releasing the brake upon the closing of said motor switchto start the motor and .electroresponsire switch mechanism under thecontrolof the said motor switch, the generated Voltage of the motor, thecurrent in the brake winding and the current in the said dynamic brakecircuit for'automatically controlling the said brake winding upon theopening of said motor switch to effect a gradual reduction 01' thecurrent in the brake winding for an interval after the opening of themotor switch and to then completely deenergize 14c. In combination, adriving motor ar ranged to be connected to a source of supply,a pair ofdirectional switches, separately operable to energize the motor from thesource for each directionot operation, a normally applied mechanicalbrake having a winding'arranged to' be connected to a 1 sourcefoi supply.for releasing the brake, V

mechanism for electrores'ponsiv'e switch controlling the connection ofsaid winding to its source, and for controlling the degree ofenergization of the winding, a pair of relays energized responsively tothe generated potential 01" the motor and to the cur rent in the bralrewinding for controlling the said switch mechanism, and connectionswhereby upon the closing of a selected one of said directional switchesthe motor and the brake winding are energized, upon the opening of saiddirectional switch a selected one of said relays operates to maintainthe connection of the brake winding to its source and e"cct a furtherreduction of the current in the brake winding an interval after theopening of the directional switch.

15. In combination, a driving motor arranged to be connected to a sourceof supply, a dynamic braking circuit for the motor, a normally appliedmechanical brake having a winding arranged to be connected to the sourcefor releasing the brake, a line switch for connecting the motor to thesource, means for reducing the current in said winding to effect apartial application of the brake, electroresponsive switch mechanismunder the control of said line sw tch, the generated voltage of themotor, the current in the brake winding and the current in the motordynamic brake circuit for controlling the said means and the connectionof the brake winding to the source, and connections whereby upon theopening of said line switch the said electroresponsive switch mechanismmaintains the said winding connected to the source and effects areduction of the current in the brake winding circuit to efiect apartial application of the brake for an interval, the brake winding issubsequently automatically disconnected from the source, leaving thebrake winding in a local circuit to further increase the application ofthe brake, and the said local circuit is opened when the motor haspractically stopped rotating to effect a complete application of thebrake.

16. In combination. a driving motor arranged to be connected to a sourceof supply, a dynamic-braking circuit for the motor, a normally appliedmechanical bralre having a winding arranged to be connected to thesource for releasing the brake, a line switch for connecting the motorto the source, electroresponsive switch mechanism under the control ofsaid line switch for connecting the brake winding directly to the sourceto release the brake upon the closing of the line switch and forestablishing a shunt to the brake winding for reducing the energizationof the winding upon the openin of said line switch, a relay governedjointly by the generated voltage of the motor and the current in saidwinding for maintaining the connection of said winding to the sourceafter the opening of said line switch and for automaticallydisconnecting the winding from the source an interval after the openingof said line switch, leaving the winding connected in a local circuit tofurther reduce the energization of the winding, and a relay governed bythe current in the motor dynamic brake circuit for opening the saidlocal circuit to ei'iect a full application of the brake when the motorhas practically stopped rotating.

1?. In combination, a driving motor arranged to be connected to a sourcof supply, a dynamic braking circuit supplied with current from themotor armature to reduce the motor speed when the motor is disconnectedfrom the source, a normally applied mechanical brake having a windingarranged to be connected to the source for releasing the brake, a pairof reversing switches for connecting the motor to the source foroperation in each direction, a resistance having a plurality of sectionsfor reducing the current in the brake winding, a plurality ofelectromagnetic switches for controlling the connection of the brakewinding to the source and for controlling the said resistance toregulate the degree of application of the brake, a pair ofelectromagnetic relays jointly controlled by the generated voltage ofthe motor and the cur rent in the brake winding for controlling aportion of said electromagnetic switches to control the connection ofthe brake winding to the source of supply, a relay energizedresponsively to the current in the motor dynamic brake circuit forcontrolling the brake winding circuit, and connections whereby uponclosing either of said reversing switches the motor and the brakewinding are connected to the source and a section of said resistance isincluded in the brake winding circuit after the release of the brake toreduce the heating of the brake winding, subsequently opening the saidre versing switch disconnects the motor from the source of supply andconnects an additional section of said resistance in series with thebrake winding and the remainder of the resistance in shunt to th brakewinding, the brake winding is subsequently disconnected from the sourceof supply by the operation of one of said pair of relays, leaving thebrake winding in a local circuit to effect a further application of thebrake, and the said local circuit is opened under the control of saidrelay responsive to the current in the motor dynamic brake circuit toeffect a full application of the brake when the motor has substantiallystopped rotating. i

In witness whereof I have hereunto set my hand this 13th day ofFebruary, 1925.

BENJAMIN W. JONES

